The sea otter’s warm secret

Most marine mammals carry their own insulation on the inside: a thick layer of blubber between skin and muscle. Sea otters do not. They spend their lives in cold coastal water with nothing but fur between them and the sea — and it works because that fur is extraordinary.

A coat with no equal

According to the IUCN Otter Specialist Group, the sea otter has the densest fur of any mammal. With no blubber to fall back on, that coat is the animal’s main protection against cold water.

It also explains why oil is so dangerous to them. When oil gets into a sea otter’s fur, the fur loses its insulating power, and an otter caught in a spill can struggle to stay warm in the cool ocean.

Small animal, large appetite

Keeping warm this way takes energy, and sea otters are busy eaters. According to the IUCN factsheet, they feed on more than a hundred different prey species, from sea urchins and clams to mussels and crabs.

Hard shells are not much of a barrier. The IUCN notes that sea otters have learned to use tools to help them eat — a rare skill among mammals.

The animal that holds a forest together

Here is where the story widens. Off parts of the Pacific coast, sea otters live among kelp forests: towering stands of large brown algae that, as NOAA describes, give food and shelter to thousands of species of fish, invertebrates and marine mammals.

Sea urchins graze on kelp. When nothing keeps their numbers in check, they can strip an underwater forest bare. Sea otters eat urchins. Conservation group Oregon Wild notes that sea otters have been shown to help maintain — and even help recover — kelp forests by keeping urchin populations down.

That outsized effect is why ecologists call the sea otter a keystone species: an animal whose influence on its habitat is far larger than its numbers would suggest. Remove it, and the whole structure can change.

A history of loss and return

The same fur that keeps sea otters alive once nearly wiped them out. During the international fur trade of the eighteenth and nineteenth centuries they were hunted close to extinction, and in some places they disappeared entirely. Oregon Wild reports that the last known otter in Oregon was killed in 1907.

Populations have since partly recovered, though not everywhere, and the species still faces threats — pollution and oil spills among them. In California, NOAA notes that the Elkhorn Slough reserve alone is home to more than a hundred sea otters, a reminder of what protection can make possible.

Why it matters

The sea otter is a good animal to start with because it shows how connected a coastline is. A fur coat, a hungry mammal, a spiny urchin and a forest of algae turn out to be one story. Look after one part of it, and the rest has a better chance too.